1. Field of the Invention
This invention relates to an electrophotographic process for recording and preserving an electrostatic latent image developed by wet development.
2. Description of the Related Art
In the field of image formation, a system in which a uniformly charged photoconductor is selectively irradiated with light as a function of image signals and an electrostatic latent image thus formed is developed is generally termed an electrophotographic process. This process may be roughly classified into either a dry developing method or a wet developing method.
The dry developing method has an advantage in that it is superior in the ease of handling and the stability of the toners used for development, since it is based on the principle that colorant particles are simply spread and affixed to an electrostatic latent image. However, dry developing is second to the wet development method in meeting the recent demand for high quality images, as exemplified by a video printer for taking an electronic still photograph.
On the other hand, the wet developing method makes use of a liquid developer which is produced by dispersing the dyestuff or pigment as the colorant in an insulating medium. According to the wet developing method, a resolution and gradation comparable to those of a silver halide photograph may be obtained, while the image exhibits superior weatherability when a pigment is used as the colorant.
The developer used in the conventional wet developing method contains an insulating medium which is liquid at room temperature, such as "Isopar G", a saturated hydrocarbon produced by Esso Inc., so that it is naturally liquid at room temperature (see FIG. 23).
However, the developing method employing a developer 5' which is liquid at room temperature is inconvenient to use since the developer can be handled only with difficulty and frequent maintenance is required for maintaining stable image formation.
In the preservation and supply of the wet developer, disadvantages are presented in connection with changes in the concentration thereof caused by cohesion or precipitation of the colorant particles and disposal of waste liquids.
The Japanese Kokai (Published Application) No. 25670/1988 discloses a method of developing an electrostatic latent image formed on the surface of a sensitized material wherein a toner is solidified and applied under pressure to the peripheral surface of a developing roll and the thus coated toner is dissolved by a developer and caused to flow into a space between the sensitized material and the developing roll.
In this reference, a developer such as "Isopar" is required for dissolving the solid toner, while a stable image cannot be obtained unless the supply of the developer is adjusted constantly.
For recording and preserving the electrostatic latent image in the visible form, it is preferably transferred to a suitable substrate. However, the conventional wet developing method is not necessarily suited to the purpose of forming a high quality image since the adsorption between the colorant particles and the sensitized material is so strong that the transfer efficiency is thereby lowered.